(a) Field of the Invention
The present invention relates to a cathode-ray tube (CRT) having a faceplate panel, and more particularly, to a CRT faceplate panel for producing a uniform and clear visual image across the entire area of a viewing screen.
(b) Description of the Related Art
Generally, CRTs are designed to reproduce a picture image on a screen of a faceplate panel by exciting phosphors coated on an interior surface of the faceplate panel with electron beams emitted from an electron gun and passing through apertures of a color-selecting shadow mask. The shadow mask ensures that each electron beam lands on the correct phosphor.
The faceplate panel is usually formed with a transparent glass plate having curved interior and exterior surfaces. These curved surfaces enable the panel to withstand the high-vacuum in the CRT and facilitate the landing of the electron beams on the phosphor screen.
However, such a faceplate panel involves a relatively broad light-reflecting exterior area in peripheral portions, thereby deteriorating the brightness of those areas and distorting the appearance of the picture.
To remedy this problem, a glass plate having flat interior and exterior surfaces has been developed to be used for the CRT panel. Such a panel employs a flat tension mask to perform the color-selecting function, the flat tension mask corresponding to the flat interior surface of the panel. The flat tension mask has predetermined horizontal and vertical tensional strengths to prevent the occurrence of a doming phenomenon.
However, in this type of panel, the visual images realized through the phosphor screen and refracted on the panel appear depressed to the user in the center portion of the viewing screen. The problem becomes more severe with larger-sized screens.
To overcome this drawback, Japanese Patent Laid-Open Publication Nos. H6-44926 and 6-36710 introduce a CRT faceplate panel, which is flat on an exterior surface but curved on an interior surface. However, the images realized through these inventions appear bulged outward. Further, because the peripheral portions of the panel are considerably thicker than the center portions, the brightness of the screen is deteriorated.
It is an object of an embodiment of the present invention to provide a CRT faceplate panel for producing a uniform visual image across the entire area of a viewing screen.
It is another object of an embodiment of the present invention to provide a CRT faceplate panel having an optimum light transmission rate to realize a clear visual image across the viewing screen.
It is still another object of an embodiment of the present invention to provide a CRT having a faceplate panel for producing a clear visual image across the viewing screen.
In order to achieve these objects and others, an embodiment of the CRT faceplate panel includes a faceplate panel having a substantially flat exterior surface and a substantially concave interior surface, and a phosphor screen formed on the interior surface of the faceplate panel. The phosphor screen has a horizontal axis, a vertical axis and a diagonal axis. A length from a central portion of the phosphor screen to a point where a vertical side line of the phosphor screen intersects the horizontal axis is less than a length from the central portion of the phosphor screen to a point where the vertical side line intersects the diagonal axis.
The faceplate panel comprises an effective screen corresponding to the phosphor screen. That is, the effective screen comprises a horizontal axis, a vertical axis and a diagonal axis, wherein a length from a central portion of the effective screen to a point where a vertical side line of the effective screen intersects the horizontal axis is less than a length from the central portion of the effective screen to a point where the vertical side line intersects the diagonal axis.
The cathode ray tube further comprises a shadow mask placed behind the faceplate panel, the shadow mask having an effective electron beam-passing area on which a plurality of apertures are formed, in which the effective beam-passing area of the shadow mask comprises a horizontal axis Hs, a vertical axis Vs and a diagonal axis Ds, wherein a length Hsd from a central portion of the effective beam-passing area to a point where the vertical side line of the effective beam-passing area intersects the horizontal axis Hs is less than a length from the central portion of the effective beam-passing area to a point where the vertical side line of the effective beam-passing area intersects the diagonal axis Ds.